The present invention relates to an apparatus and method for manufacturing a semiconductor device, particularly, to a pretreatment in preparation for a selective CVD (Chemical Vapor Deposition) treatment for burying W (tungsten) in a contact hole to achieve an electrical connection between a silicon wafer and a conductive layer formed above the wafer surface.
In the manufacture of a semiconductor device having a multi-wiring layer structure, a conductive plug material, e.g., W, is buried in general in a contact hole such as a via-hole connecting upper and lower wiring layers so as to improve the reliability of the upper wiring layer made of, for example, aluminum. On the other hand, where W is buried by selective CVD in a contact hole for electrically connecting a first conductive layer, such as a diffusion region formed in a semiconductor substrate, e.g. a Si layer, to a second conductive layer formed above the first conductive layer, it is necessary to form a barrier metal layer on the surface of the first conductive layer (or bottom of the contact hole) in order to prevent the buried W layer from biting the Si layer.
FIGS. 1A to 1F are cross sectional views collectively showing schematically the conventional selective CVD method for burying W in a contact hole. On the other hand, FIG. 2 a flow chart schematically showing the flow of the required treatments. In the first step, a contact hole 3 is formed in an insulating film 2 formed to cover the surface of a silicon wafer 1, as shown in FIG. 1A. Then, a titanium (Ti) film 4 and a titanium nitride (TiN) film 5 are formed successively by a sputtering method on the entire surface including the contact hole 3, as shown in FIG. 1B. The TiN film 5 acts as a cap material serving to prevent the Ti film 4 from being nitrided or oxidized in the subsequent annealing step. Then, annealing is applied under a nitrogen gas atmosphere at 200.degree. C. or higher so as to achieve silicidation at the interface between the silicon wafer 1 and the Ti film 4. As a result, a barrier metal layer 6 made of TiSi.sub.x is formed at the bottom region of the contact hole 3, as shown in FIG. 1C.
After formation of the TiSi.sub.x film 6, the excess Ti film 4 and TiN film 5, which were not involved in the above-noted silicidation, are removed. In the subsequent step, a native oxide (SiO.sub.2) film 7 formed on the surface of the TiSi.sub.x film 6 as shown in FIG. 1D is removed as a pretreatment in preparation for the selective CVD treatment for burying W in the contact hole 3. Then, a W film 8 is buried in the contact hole 3 by the selective CVD treatment such that the W film 8 is in direct contact with the TiSi.sub.x film 6 having the native oxide film 7 removed from the surface, as shown in FIG. 1E. Finally, a second conductive layer 9 acting as an upper wiring layer is formed on the entire surface, as shown in FIG. 1F, thereby to achieve a multi-wiring structure in which the silicon wafer (first conductive layer) 1 is electrically connected to the second conductive layer 9 via the W film 8 filling the contact hole 3.
In the conventional method, however, it is necessary to remove the excess Ti film 4 and the TiN film 5 after formation of the TiSi.sub.x film 6, as shown in FIG. 2. What should also be noted is that the TiSi.sub.x film 6 soon after formation is exposed to the air atmosphere before the selective CVD treatment for burying W in the contact hole 3, with the result that the native oxide film 7 is formed on the surface of the TiSi.sub.x film 6. Naturally, it is absolutely necessary to remove the native oxide film 7 before deposition of the W film 8. Further, a sputtering method is employed for forming the Ti film 4 and the TiN film 5. It should be noted in this connection that, where the contact hole 3 has a high aspect ratio, i.e., a ratio of the height to the diameter, the sputtered particles fail to reach sufficiently the bottom of the contact hole 3, resulting in failure to form a TiSi.sub.x film of a high quality.